This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-187023, filed Jun. 30, 1999; and No. 2000-187995, filed Jun. 22, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a semiconductor device having a wiring structure capable of preventing a short-circuiting between a W damascene wiring and a plug and a method of manufacturing the same.
A buried tungsten wiring structure (W damascene wiring structure) is used nowadays in many cases in a semiconductor device such as DRAM. FIG. 15 shows the conventional W damascene wiring structure, comprising an interlayer insulating film 81, a barrier metal layer 82, a W wiring 83, and a cap insulating film 84. The barrier metal film 82 is formed of a titanium nitride film.
In the W damascene wiring structure shown in FIG. 15, the entire W wire 83 is covered with the barrier metal film 82 and the cap insulating film 84, making it possible to prevent an adverse effect from being given to the device by the tungsten diffusion.
In the case of using the W damascene wiring structure shown in FIG. 15, the aligning mark cannot be recognized because the surface of the interlayer insulating film 81 is not planarized and, thus, deviation in alignment tends to take place. Therefore, where a contact hole is made in the interlayer insulating film 81 for forming a plug 85, a short-circuiting tends to take place between the W wiring 83 and the plug 85.
In order to overcome the above-noted problem, it is conceivable to employ the wiring structure as shown in FIG. 17A or FIG. 17B. In the wiring structure shown in each of these drawings, the barrier metal film 82 in an upper portion of the wiring groove, said barrier metal film 82 causing a short-circuiting problem, is removed.
In order to realize the wiring structure shown in FIG. 17A, the barrier metal film 82 and the W wiring 83 must be non-selectively etched as shown in FIG. 18A. Alternatively, it is necessary to selectively etch the barrier metal film 82 relative to the W wiring 83, as shown in FIG. 18B. Likewise, similar non-selective or selective etching must be performed for realizing the wiring structure shown in FIG. 18B.
The etching includes a dry etching and a wet etching. The dry etching includes an anisotropic etching called RIE (Reactive Ion Etching) and an isotropic etching called CDE (Chemical Dry Etching). However, it is difficult to perform the non-selective etching and the selective etching shown FIGS. 18A and 18B by these etching methods. Particularly, it is substantially impossible to achieve the selective etching shown in FIG. 18B.
It should also be noted that a CF-based gas, which produces a serious problem in terms of the earth environment, is used as a raw material gas in the dry etching. Further, a wet etching is performed after the dry etching for removing the by-products of the dry etching. It follows that the dry etching process is disadvantageous in the number of process steps required and the cost, compared with the wet etching process.
On the other hand, it is known to the art concerning the wet etching that tungsten and titanium nitride can be etched by chemicals having an oxidizing power. To be more specific, tungsten and titanium nitride can be dissolved in hydrochloric acid mixed with a hydrogen peroxide solution, i.e., hydrochloric acid allowed to produce an oxidizing power.
In general, a mixed solution of hydrochloric acid and a hydrogen peroxide solution is used as a cleaning solution and called SC2. In many cases, each of hydrochloric acid and hydrogen peroxide solution available on the market has a concentration of about 30 to 35%. These hydrochloric acid and hydrogen peroxide solution are mixed at a mixing ratio of 1:1 and the mixture is diluted with pure water in an amount 5 to 6 times as much as the amount of the original mixture for use as an etchant, as disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 10-64866, Japanese patent Disclosure No. 8-153788 and Japanese Patent Disclosure No. 9-64006. Incidentally, the molar ratio of the hydrogen peroxide to hydrogen chloride in the hydrochloric acid is about 1.
If tungsten and titanium nitride are etched with the etchant described above, the etching rate of the tungsten is about 4 to 5 times as high as that of titanium nitride. Particularly, tungsten can be etched with only the hydrogen peroxide solution that is weakly acidic. It follows that in the conventional wet etching using a mixed solution of hydrochloric acid and a hydrogen peroxide solution, it was difficult to increase the selectivity ratio of titanium nitride relative to tungsten to exceed 1.
Also, the cleaning using a mixed solution of sulfuric acid and a hydrogen peroxide solution is called an SP cleaning, which is generally employed for removing a resist film. Disclosed in, for example, Japanese Patent Disclosure No. 10-50986 is an etching method for selectively etching a TiN film relative to a W film, a Cu film or a TiSi film by using the mixed solution noted above. In this method, it is possible to achieve at least 20 nm/min of the TiN film etching rate and at least 7 nm/min of the W film etching rate by using a mixed solution consisting of 1 part of sulfuric acid and 6 parts of a hydrogen peroxide solution and by setting the process temperature at 130xc2x0 C. However, if the process temperature exceeds 100xc2x0 C., it is difficult to use a pure water as a diluent, leading to an increased amount of the mixed solution consisting of sulfuric acid and hydrogen peroxide solution used as the etchant.
Another difficulty is brought about in the case of the batch treatment in which a plurality of wafers are processed simultaneously by employing the etching method described above. Specifically, in the case of etching a thin TiN film that is about 20 nm thick, it is difficult to achieve a uniform etching because the TiN film exhibits a high etching rate. A similar etching method, which is disclosed in Japanese Patent Disclosure No. 9-293727, also gives rise to a similar problem.
An object of the present invention is to provide a method of manufacturing a semiconductor device, which permits easily performing a selective etching and a non-selective etching in a tungsten-titanium nitride system.
Another object of the present invention is to provide a semiconductor device having a wiring structure that permits preventing a short-circuiting between a W damascene wiring and a plug, which can be easily achieved by the method of the present invention for manufacturing a semiconductor device.
According to a first aspect of the present invention, which is intended to achieve the objects described above, there is provided a semiconductor device, comprising a silicon oxide film having a wiring groove, a silicon nitride film formed on a side wall of the wiring groove and not filling the side wall, a first tungsten film formed to extend from the bottom of the wiring groove to reach a central portion of the side wall of the wiring groove and thinner in the side wall portion than the central portion of the wiring groove, a titanium nitride film formed between the first tungsten film and the side wall of the wiring groove, a second tungsten film formed between the titanium nitride film and the first tungsten film and thinner than the first tungsten film, and a silicon nitride film formed on the second tungsten film to fill the wiring groove.
According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising an etching step using a mixed solution containing hydrochloric acid and a hydrogen peroxide solution, the molar ratio of hydrogen peroxide in the hydrogen peroxide solution to hydrogen chloride in the hydrochloric acid being 1/100 or less.
According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising an etching step for selectively etching titanium nitride relative to tungsten by using a mixed solution containing hydrochloric acid and a hydrogen peroxide solution, the molar ratio of hydrogen peroxide in the hydrogen peroxide solution to hydrogen chloride in the hydrochloric acid being 1/10 or less.
It is desirable for the molar ratio of hydrogen peroxide to hydrogen chloride to be at least 1/10,000 and, more desirably, to fall within a range of between 1/10,000 and 1/100. It is also desirable for the temperature of the mixed solution to be at least 70xc2x0 C.
According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, wherein titanium nitride is selectively etched relative to tungsten by using a mixed solution containing sulfuric acid, hydrogen peroxide and water under the condition that the mass of hydrogen peroxide within the mixed solution is not larger than 1,000 mg per liter of the mixed solution (or the mass percentage of the hydrogen chloride based on the solution is not higher than 0.35%).
According to the research conducted by the present inventors, the selectivity ratio of titanium nitride relative to tungsten can be markedly improved by using a mixed solution in which the molar ratio of hydrogen peroxide to hydrogen chloride is not larger than 1/10 (or the mass percentage is not higher than 0.35%), particularly, not larger than 1/100, (or the mass percentage is not higher than 0.035%) which is markedly smaller than in the conventional etchant.
The molar ratio (or mass percentage) noted above correspond to the selectivity ratio noted above. Therefore, in order to obtain a predetermined selectivity ratio, it does not suffice to set the molar ratio at 1/100 or lower (or the mass percentage 0.35% or lower). In other words, it is necessary to control the amounts of hydrogen chloride and hydrogen peroxide within the solution so as to obtain a predetermined molar ratio not larger than 1/100 (or the mass percentage not higher than 0.35%).
It has also been found that tungsten and titanium nitride can be etched non-selectively by using a mixed solution in which the molar ratio of hydrogen peroxide to hydrogen chloride falls within a range of between 1/10 and 4/10. It follows that the present invention using the particular mixed solution as an etchant makes it possible to realize easily both a selective etching and non-selective etching of a tungsten-titanium nitride system and also makes it possible to realize a wiring structure that permits preventing a short-circuiting between the W damascene wiring and the plug.
Further, according to the research conducted by the present inventors, it is possible to markedly improve the selectivity ratio of titanium nitride relative to tungsten in selectively etching titanium nitride relative to tungsten by using an etchant consisting of a mixed solution containing sulfuric acid, hydrogen peroxide and water by controlling the mass of hydrogen peroxide in the mixed solution at 1,000 mg or less, particularly, 300 mg or less, per liter of the mixed solution. Naturally, the present invention using the particular etchant makes it possible to realize easily a selective etching of titanium nitride relative to tungsten. What should also be noted is that the etching of a high selectivity is scarcely deteriorated even in the case of using the mixed solution at a high temperature (typically at 80xc2x0 C. or higher), compared with the etching using a mixed solution containing hydrochloric acid.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.